Data with an outlier

In the ten o'clock section the height versus heart rate data included an outlier. An outlier is a data point that is far away from the other data points. There was no outlier in the eight nor in the nine o'clock section.

There can be more than one outlier. Not all data will have outliers. On a graph an outlier is often far from the other points on the graph. In the graph there is an outlier. The data point for the outlier is (42 inches tall, 92 beats per minute). On the graph the point is at the upper left, all alone. 

The outlier represents something that is very different from the average college student. Remember that the graph is height versus heart rate. The outlier has an usual height, 42 inches, and  a high heart rate, 92 beats per minute. 

The outlier

As the ten o'clock class is aware, the outlier happened to be my niece who had joined the ten o'clock class. She is four years old, hence the unusual height and heart rate. Outliers are an indication of an unusual situation, of something very different about the data for that one point. 

Do be careful if you obtain an outlier in data you are working with - sometimes the outlier is the result of a data entry error. If the outlier is real, however, then that data point is unusual relative to the other data. Understanding why a data point is an outlier is sometimes important. 

Note that if the outlier is a valid sample data point for your sample, then one would keep the outlier in your data. The 213 jump data point in a data set from a jump rope contest is a valid data point.

One other note for readers of this blog: the high heart rates for the college students, taken while sitting, in some instances reflect the effect of betel nut chewing prior to class. In an earlier class a student had a 110 bpm sitting heart rate due to having just finished a nut.

To see the original data from all three sections, refer to the Google docs spreadsheet.